1. Technical Field
The present invention relates to a printing device, a printing device control program and method, and a printing data generation device, program, and method for use with printers of facsimile machines, copying machines, OA equipment, and others. More specifically, the present invention is suitable for use with a printing device of an ink jet type that is capable of text and image rendering onto a printing paper. (printing medium) through discharge of liquid ink particles of various colors, a control program and method for such a printing device, and a printing data generation device, program, and method.
2. Related Art
Described below is a printing device, specifically a printer of an ink jet type (hereinafter, referred to as ink jet printer”).
Because ink jet printers are relatively inexpensive and they easily achieve high-quality color printing, ink jet printers have become widely popular not only for office use but also for personal use particularly with the spread of personal computers, digital cameras, and the like.
Such an ink jet printer generally performs text and image rendering on a printing medium (paper) using a moving element in a predetermined manner so that any desired printing is achieved. More in detail, the moving element referred to as a carriage includes an ink cartridge and a printing head as a piece, reciprocating relative to the printing medium in a direction perpendicular to the paper feeding direction, and discharging (ejecting) liquid ink droplets in the form of dots from the nozzles provided to the printing head. If the carriage is provided with ink cartridges of four colors, i.e., black, yellow, magenta, and cyan, and each corresponding printing head, full-color printing becomes possible in addition to monochrome printing by color mixture. Better still, ink cartridges of six, seven, or eight colors additionally with light cyan, light magenta, and others are also in practical use.
There is a problem with ink jet printers that perform printing with the printer head reciprocating on the carriage in the direction perpendicular to the printing paper. That is, to derive a clearly-printed page, the printing head requires frequent reciprocating movements, e.g., several tens to a hundred or more. This results in a drawback of a longer printing time as compared with other types of printing devices such as electrophotographic laser printers or others, e.g., copying machines. Note here that ink jet printers of this type are generally referred to as “multi-path printers” or “serial printers”.
On the other hand, with an ink jet printer that does not use a carriage but rather a long printing head having the same width as that of the printing paper or longer, there is no need to move the printing head in the width direction of the printing paper. This accordingly allows printing with a single scan, i.e., a single path, favorably leading to high-speed printing as with laser printers. What is better, this eliminates the need for a carriage with a printing head, and a drive system for moving the carriage, thereby reducing the size and weight of the cabinet of the printer, and the noise to a considerable degree. Note here that ink jet printers of this type are generally referred to as “line-head printers”.
The issue with such ink jet printers is the manufacturing deviation observed in the printing head that serves an essential role for the printer. The manufacturing deviation results from the configuration of the printing head, carrying very small nozzles of about 10 to 70 μm in diameter in a line at regular intervals, or in a plurality of lines in the printing direction. In such a configuration, a nozzle may be partially misaligned so that the ink discharge direction is incorrectly angled, or the nozzles may not be correctly disposed as they are expected to be so that the nozzles resultantly fail in forming dots at their ideal positions, i.e., ink deflection. Because the nozzles often show a wide range of variation in the ink amount, if the variation is too much, the ink amount to be discharged from the nozzle is considerably large or small compared with the ideal amount of ink.
As a result, an image part printed by such a faulty nozzle suffers a printing failure, i.e., a so-called banding (streaking) problem, resultantly reducing the printing quality considerably. More in detail, with ink deflection, the dot-to-dot distance between dots formed by any adjacent nozzles becomes non-uniform. When such a dot-to-dot distance is longer than usual, the corresponding part suffers from white streaks when the printing paper is white in color. When the dot-to-dot distance is shorter than usual, the corresponding part suffers from dark streaks. When the amount of ink coming from any of the nozzles is not ideal and is a lot, the part for the nozzle suffers from dark streaks, and when the amount of ink is little, the part suffers from white streaks.
Such a banding problem is often observed in “line head printers” in which a printing head or a printing medium is fixed, i.e., printing with a single scan, compared with the above-described “multi-path printers” (serial printers) This is because the multi-path printers are adopting the technology of making white streaks less noticeable utilizing frequent reciprocating movements of the printing head.
For the purpose of preventing printing failures caused by the banding problem, research and development has been actively conducted from the hardware perspective, e.g., improving the manufacturing technology of the printing head, or improving the design thereof. However, from the perspective of manufacturing cost, the printing quality, the technology, or others, it is found difficult to provide a printing head perfectly free from the banding problem.
In consideration of the above, the currently-available technology for correcting the banding problem is adopting a so-called software technique such as printing control as described below in addition to such improvements from the hardware perspective as described above.
As an example for such a technology, Patent Document 1 (JP-A-2002-19101) and Patent Document 2 (JP-A-2003-136702) describe the technology as a measure against the ink amount variation of the nozzles, and ink discharge failures. More in detail, parts of lower density are applied with shading correction so that any head variation is handled, and parts of higher density are provided with substitution color, e.g., cyan or magenta for printing in black, so that the banding problem is corrected or any ink amount variation is made less noticeable.
Patent Document 3 (JP-A-2003-63043) describes the technology of generating filled-in images, i.e., images being solidly and completely filled, using all provided nozzles. That is, for filled-in images, any nozzles in the vicinity of pixels in charge of any discharge-faulty nozzle(s) are increased in ink amount for discharge.
Patent Document 4 (JP-A-5-30361) describes the technology of preventing the banding problem with a process of feeding back any variation observed to the ink amount coming from the nozzles through error diffusion so that the variation is absorbed.
The concern here is that, with the technology of correcting the banding problem or reducing the variation of nozzles using substitution colors as related arts found in Patent Document 1 and 2, any processed parts are changed in hue. In consideration thereof, such technologies are not suitable for printing required to be high in image quality and printing quality as color photograph printing.
Another issue is with the technology of allocating information about any discharge-faulty nozzles to the right and left thereof to prevent white streaks in parts high in density. If this technology is applied to solve the above-described ink deflection problem, white streaks are actually reduced but the banding problem still remains unsolved in parts high in density.
The related art of Patent Document 3 causes no problem with printing subjects if they are filled-in images, but cannot be used if printing subjects are of halftone. The technology of using substitution colors may serve well for thin lines. However, if with an image of many colors, i.e., one color next to another, the technology also fails to solve the problem of hue change in the image.
The related art of Patent Document 4 also raises an issue of complicating the feeding-back process that is expected to be appropriately executed against the problem of not deriving ideal dot formation details, and such an issue is difficult to solve.